Generally, it is desirable to protect not only a passenger in a vehicle but also a pedestrian from being injured due to a collision of the vehicle. As a protection device for the pedestrian in the collision, it is proposed to reduce an impact on the pedestrian when the pedestrian collides with the vehicle and falls onto a bonnet of the vehicle. In this case, it becomes important to detect a collision between the vehicle and the pedestrian for the protection device.
For example, a collision detection unit for a vehicle is disclosed in JP-T-2005-538881 (US 2005/0116817 A1). In this case, the vehicle is provided with a front sensor which is constructed of a contact sensor and has at least one cavity. The each cavity has therein a sensing element, by which the collision (of vehicle) related to the deformation of the cavity is detected.
However, in this case, the vehicle is provided with an additional sensor for detecting the collision between the vehicle and the pedestrian. That is, the front sensor disclosed in JP-T-2005-538881 is not suitable for the detection of the collision between the vehicle and the pedestrian.
With a reference to the above-described detection method, a collision detection apparatus for detecting a collision between the vehicle bumper and the pedestrian is considered, as shown in FIGS. 6 and 7. In this case, a space 20 which is sealed (i.e., hermetic space such as cavity in JP-T-2005-538881) is arranged between a bumper reinforcement member 1 and an absorber 2 positioned at a vehicle front side of the bumper reinforcement member 1. The collision of the pedestrian is detected based on a variation in a pressure in the space 20 by a pressure sensor 4.
In this case, it is required to maintain the hermeticity of the space 20 because the collision is detected according to the variation of the pressure of the closed space 20. That is, it is necessary for the bumper reinforcement member 1 and the absorber 2 are joined to each other over the whole circumference thereof.
Generally, the bumper reinforcement member 1 and the absorber 2 of the vehicle are constructed of metal such as iron or the like, and joined to each other by spot-welding. In order to maintain the hermeticity of the space 20 which is defined between the bumper reinforcement member 1 and the absorber 2, it is considered to weld the whole circumference of the joint therebetween.
However, the welding over the whole circumference will cause not only a cost increase but also a change of a squash property (deformation property in collision) of the absorber 2. Thus, a protection performance of a pedestrian foot portion of the absorber 2 in the collision with the pedestrian will be deteriorated. Moreover, the deformation of the absorber 2 may become insufficient. Thus, it is difficult to detect the collision of the vehicle with a satisfactory detection accuracy.